1. Field of the Invention
This invention relates to electromagnetic applicators and, more particularly, to an electromagnetic transmission/receiver apparatus and method for directly coupling electromagnetic energy into a material with minimal external radiation.
2. The Prior Art
Recent statistics show that pulmonary and cardiopulmonary diseases are responsible for more than three million hospital admissions and 30,000 deaths every year in the United States. Pulmonary abnormalities are virtually always associated with changes in lung water content or distribution. Most workers agree that there is no single, nondestructive method available to detect accurately early changes in lung water content. Presently available techniques to measure such changes are generally insensitive, complicated, and clinically undesirable, particularly in detecting the important interstitial phase of acute pulmonary edema, before the onset of alveolar flooding, and before there is significant interference with gas exchange.
For a clinically useful technique, on the other hand, it is desirable to detect early changes in both the extravascular lung water, which strongly reflects most pulmonary abnormalities, and the intravascular compartment. Recently, the use of the electromagnetic methods to detect changes in lung water content have shown promising initial results, particularly for detecting small variations in water content. Particularly at microwave frequencies, changes in the dielectric properties of tissue are closely related to the amount of water present. Electromagnetic techniques, therefore, basically utilize changes in the permittivity and conductivity of the lung tissue to detect changes in lung water content. This method has the advantage of using highly penetrating electromagnetic signals rather than ultrasonic signals which are both highly attenuated and dispersed in the lung. Furthermore, electromagnetic techniques have the potential for continuous monitoring of patients in intensive care units, such as those with heart failure or extensive burns.
Before utilizing microwave or any other suitable electromagnetic energy method in clinical applications, the fundamental questions regarding its sensitivity, the possibility of developing a clinically adequate system to transmit and receive the signal, and its usefulness in monitoring changes as well as absolute values of lung water should be first carefully examined. An electromagnetic energy applicator that is adequate for clinical use should satisfy the following criteria:
1. It should be small, flat, and light-weight and hence convenient for placement on critically ill patients. PA1 2. It should provide maximum coupling to the body with minimal external radiation, in order to minimize its sensitivity to the external surroundings.
These requirements, however, are difficult to satisfy in a radiation-type applicator such as the commonly used, open-ended waveguides and horns because of the associated radiation leakage. Furthermore, open-ended waveguides and horns tend to be too large at the operating frequency. Attempts to reduce the dimensions by using dielectric-loaded waveguides or to minimize the leakage by using flanged waveguides were found to be ineffectual because of the resulting excess weight and size.
It would, therefore, be an improvement in the art to provide a novel electromagnetic energy transmission/receiver apparatus and method for coupling electromagnetic energy into tissue while substantially reducing external leakage of the energy. It would also be an improvement in the art to provide a relatively small, flat, and light-weight electromagnetic energy transmission apparatus thereby rendering the applicator convenient for placement on critically ill patients. It would be a further improvement in the art to provide a method for minimizing external leakage of electromagnetic energy by coupling the electromagnetic energy into the tissue with an open transmission line. Such a novel apparatus and method is disclosed and claimed herein.